Systems and methods for managing a ue-to-network relay

ABSTRACT

Method and systems for managing a communication link. One or more indicators of an expected service interruption associated with a communication link is determined. The communication link may be a link between a relay and a communication target and/or a link between the relay and a user equipment (UE). In response, the UE initiates one or more actions to reduce or avoid the expected service interruption.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of and claims priority fromU.S. patent application Ser. No. 15/664,452 filed Jul. 31, 2017, whichitself is a continuation of, and claims priority to, U.S. patentapplication Ser. No. 14/794,208, filed Jul. 8, 2015. The entire contentsof each of these priority applications and are incorporated herein byreference.

FIELD

The present disclosure is related to methods and systems for managing aUE-to-network relay. In various examples, the present disclosure isrelated to methods and systems for handling service continuity in aUE-to-network relay.

BACKGROUND

Device to Device (D2D) Proximity-based Services (ProSe) refer to a setof features supporting device to device communication in the EnhancedPacket System (EPS). ProSe features include ProSe Direct Discovery,which enables proximate devices to discover each other and the servicesproved by each other, and ProSe Direct Communication. ProSe features canbe used for public safety applications (e.g. mission critical push totalk (MCPTT)) and/or for commercial applications.

ProSe Direct Communication is a mode of communication whereby userequipments (UEs) can communicate with each other directly over the PC5(UE to UE) radio interface via direct air-interfaces between two devices(also referred to as sidelink channels). This may be in contrast to theradio interface between a UE and the base station (or the rest of thenetwork), which may also be referred to as Uu.

For public safety-specific usage, ProSe Direct Communication isfacilitated by the use of ProSe User-to-Network Relays (UNRs), which areUEs that act as relays between the network (e.g., an Evolved UniversalTerrestrial Radio Access Network (E-UTRAN)) and one or more UEs notserved by the network (e.g., to provide network based services to UEswhich are out of network coverage). Also, ProSe Direct Communicationbetween two UEs not served by the network and out of each other'stransmission range may be facilitated by a ProSe UE-to-UE Relay (UUR).

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example, to the accompanyingdrawings which show example embodiments of the present application, andin which:

FIG. 1 is a schematic diagram illustrating an example system includingexample relays;

FIG. 2 is a schematic diagram of an example processing unit that may besuitable for implementing examples of the present disclosure;

FIG. 3A is a signaling diagram illustrating an example method formanaging a communication link, wherein an indicator of expected serviceinterruption may be identified by the relay;

FIG. 3B is an example message that may be transmitted to indicate anexpected service interruption;

FIG. 4 is a signaling diagram illustrating an example method formanaging a communication link, wherein an indicator of expected serviceinterruption may be identified by the base station;

FIG. 5A is a signaling diagram illustrating an example method formanaging a communication link, wherein an indicator of expected serviceinterruption may be identified by the UE;

FIG. 5B is an example status report message that may be transmitted to aUE;

FIG. 6 is a signaling diagram illustrating an example action to reduceor avoid an expected service interruption; and

FIG. 7 is a signaling diagram illustrating an example method formanaging a communication link, wherein a relay switches to operation asa UUR.

Similar reference numerals may have been used in different figures todenote similar components.

DESCRIPTION OF EXAMPLE EMBODIMENTS

In some examples, the present disclosure provides a method for managinga communication link. The method includes: detecting one or moreindicators of an expected service interruption associated with at leastone of: a communication link between a relay and a communication target;and a communication link between the relay and a first user equipment(UE); and causing a first message to be transmitted, the first messageindicating that the expected service interruption is expected to occur;the first message causing the first UE to initiate one or more actionsto reduce or avoid the expected service interruption.

In some examples, the present disclosure provides a method for managinga communication link. The method includes: receiving a status reportproviding information indicative of the quality of at least one of: acommunication link between a relay and a communication target; and acommunication link between the relay and a first user equipment (UE);determining whether a parameter included in the information falls belowa predetermined threshold or fails to satisfy a predetermined criterion;when it is determined that the parameter is below the predeterminedthreshold or fails to satisfy the predetermined criterion, determiningthat a service interruption is expected and initiating one or moreactions to reduce or avoid the service interruption.

In some examples, the present disclosure provides a system for managinga communication link, the system comprising a processor configured toexecute instructions to cause the system to: detect one or moreindicators of an expected service interruption associated with at leastone of: a communication link between a relay and a communication target;and a communication link between the relay and a first user equipment(UE); and cause a first message to be transmitted, the first messageindicating that the expected service interruption is expected to occur;the first message causing the first UE to initiate one or more actionsto reduce or avoid the expected service interruption.

FIG. 1 is a schematic diagram of an example system, in which relays areused to provide ProSe services to remote UEs. The system 100 may includean application server 105, such as a Group Communication ServiceApplication Server (GCS AS), which may function as the MCPTT applicationserver and provide MCPTT services. The application server 105 mayreceive and transmit communications via a network 110, which may be anIP-based communication network. Communications in the network 100 mayinclude multicast (i.e., point-to-multipoint) and/or unicast (i.e.,point-to-point) transmission types. Communications to and from theapplication server 105 may be passed through one or more gateways 115,such as a Public Data Network gateway (PDN GW), a Broadcast MulticastService Center (BM-SC), and/or a Multimedia Broadcast Multicast Servicesgateway (MBMS GW). The gateway 115 may in turn transmit/receivecommunications to/from one or more base stations 120, such as an EvolvedNode B (eNB, also referred to as an E-UTRAN Node B).

The application server 105, gateway(s) 115 and base station(s) 120 maybe collectively referred to as the network. The network may provideMCPTT services to UEs 125 that are within radio coverage of one or morebase stations 120. UEs 125 having this direct service may operate in amode referred to as Network Mode Operation (NMO). One or more remote UEs130 (i.e., UEs which are outside of network coverage) may receive MCPTTservices via an associated relay 135 (such as a UNR, which is itself aUE within coverage of the network), in a mode referred to as NetworkMode Operation via Relay (NMO-R).

In FIG. 1, solid arrows indicate unicast transmissions from the networkto in-coverage UEs 125, 135 over a Uu channel, dashed arrows indicatemulticast or broadcast (e.g., MBMS) transmissions from the network toin-coverage UEs 125, 135 over a Uu channel, open arrows indicatedownlink transmissions from a relay 135 to a remote UE 130 in a relayover UE-to-UE radio interface (e.g., PC5), and dotted arrows indicateuplink transmissions from a remote UE 130 to a relay 135 over UE-to-UEradio interface. Dotted lines about a base station 120 representsservice coverage provided by that base station 120. Dotted lines about arelay 135 indicate the relay coverage provided by that relay 135.

The relay 135 may be used for extending network coverage for MCPTT andother services. The relay 135 is able to connect one or more associatedremote UEs 130 to the network. The relay 135 then relays downlink (i.e.,network-to-UE) and uplink (i.e., UE-to-network) transmissions over theProSe UE-to-UE sidelink radio interface (e.g., using PC5) to itsassociated remote UE(s) 130. Thus, ProSe relays 135 may enable coverageextension for network-based services, thereby enabling remote UEs 130 toreceive the services (e.g., MCPTT services) provided by the network.

In some examples, the relay 135 may relay network communications to oneor more UEs 125 that are within coverage of the network. This may beuseful when a UE 125 is transitioning or recently transitioned from outof network coverage to within network coverage, for example. It may alsobe useful to use the relay 135 for in-coverage UEs 125 in situationswhere network resources are congested, in order to reduce the number ofUEs to which the network transmits, for example.

In some examples, the relay 135 may enable off-network MCPTT services byfunctioning as a ProSe UE-to-UE Relay (UUR), also referred to as DirectMode Operation using Relay (DMO-R). In this mode of operation, there maybe two or more remote UEs 130 associated with the relay 135. The remoteUEs 130 may be out of each other's direct transmission range, but withinthe transmission range of a common relay 135. The remote UEs 130 maythen communication with each other via the communication serviceprovided by the relay 135. In some examples, only two UEs (e.g., therelay 135 and another remote UE 130) may be communicating between eachother (e.g., without network coverage) and in this scenario, thecommunication mode may be referred to as Direct Mode Operation (DMO). Insome examples, the relay 135 may be within coverage of the network, inwhich case the relay 135 may also function as a UNR. In other examples,the relay 135 may be outside of network coverage, in which case therelay 135 may itself be a remote UE.

FIG. 2 is a schematic diagram of an example processing system 200, whichmay be used to implement: the methods and systems disclosed herein, suchas the example base station 120, UEs 125, 130 and relays 135, and theexample methods described below. The processing system 200 may be aserver or a mobile device, for example, or any suitable processingsystem, Other processing systems suitable for implementing the presentdisclosure may be used, which may include components different fromthose discussed below. Although FIG. 2 shows a single instance of eachcomponent, there may be multiple instances of each component in theprocessing system 200.

The processing system 200 includes one or more processing devices 205,such as a processor, a microprocessor, an application-specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), adedicated logic circuitry, or combinations thereof. The processingsystem 200 may also include one or more input/output (I/O) interfaces210, which may enable interfacing with one or more appropriate inputdevices 250 and/or output devices 255. The processing system 200includes one or more network interfaces 215 for wired or wirelesscommunication with a network (e.g., an intranet, the Internet, a P2Pnetwork, a WAN, a LAN, and/or a Radio Access Network (RAN)). The networkinterface(s) 215 may include wired links (e.g., Ethernet cable) and/orwireless links for intra-network and/or inter-network communications.The network interface(s) 215 may provide wireless communication via oneor more transmitters or transmit antennas and one or more receivers orreceive antennas, for example. The processing system 200 may alsoinclude one or more storage units 220, which may include a mass storageunit such as a solid state drive, a hard disk drive, a magnetic diskdrive and/or an optical disk drive.

The processing system 200 may include one or more memories 225, whichmay include a volatile or non-volatile memory (e.g., a flash memory, arandom access memory (RAM), and/or a read-only memory (ROM)). Thenon-transitory memory(ies) 225 may store instructions for execution bythe processing device(s) 205, such as to carry out the presentdisclosure. The memory(ies) 225 may include other software instructions,such as for implementing an operating system 230 and otherapplication(s)/function(s) 235. The memory(ies) 225 may also containdata 240, which may be accessed by other components of the processingsystem 200. In some examples, one or more data sets and/or module(s) maybe provided by an external memory (e.g., an external drive in wired orwireless communication with the processing system 200) or may beprovided by a transitory or non-transitory computer-readable medium.Examples of non-transitory computer readable media include a RAM, a ROM,an erasable programmable ROM (EPROM), an electrically erasableprogrammable ROM (EEPROM), a flash memory, a CD-ROM, or other portablememory storage.

There may be a bus 245 providing communication among components of theprocessing system 200, including the processing device(s) 205, I/Ointerface(s) 210, network interface(s) 215, storage unit(s) 220 and/ormemory(ies) 225, The bus 245 may be any suitable bus architectureincluding, for example, a memory bus, a peripheral bus or a video bus.

In FIG. 2, the input device(s) 250 (e.g., a keyboard, a mouse, amicrophone, a touchscreen, and/or a keypad) and output device(s) 255(e.g., a display, a speaker and/or a printer) are shown as external tothe processing system 200. In other examples, one or more of the inputdevice(s) 250 and/or the output device(s) 255 may be included as acomponent of the processing system 200.

As discussed above, the relay 135 may generally enable communicationbetween one or more UEs and a communication target (e.g., the network, acommunication system, or other entity such as other UE(s)). Depending onthe mode of operation, the relay 135 may be referred to as a UNR and/ora UUR, for example. For simplicity, the following discussion refers tothe example case where the communication target is the network (e.g.,via a base station 120), in which the relay 135 may function as a UNR.However, it should be understood that the following discussion may besimilarly applicable to cases where the communication target is anotherUE. In cases where the communication target is another UE, the relay 135may function as a UUR, and only the condition(s) applicable to thecommunication links between the relay 135 and its associated remote UEs130 may be relevant. The following discussion refers to the example casewhere the relay 135 serves one or more remote UEs 130. However, itshould be understood that the relay 135 may additionally oralternatively serve one or more UEs 125 within coverage of the network.In this respect, the matters described hereafter in relation to remoteUEs 130 may additionally or alternatively be equally applicable toin-coverage UEs 125.

In general, ProSe-capable devices (e.g. devices that support ProSe andMCPTT) are expected to be mobile. Even when the devices are not mobile,network coverage conditions may in general change over time which wouldresult in UEs going in and out of network coverage. As such, a relay 135may itself also move in and out of network coverage or may move fromcoverage by one base station 120 (e.g., a first eNB) to another basestation 120 (e.g., another eNB). Since the relay 135 is responsible forproviding network-based services to one or more remote UEs 130associated with the relay 135, when the relay 135 suffers serviceinterruption (e.g., due to mobility), this service interruption wouldaffect the associated remote UEs 130 as well. Such service interruptionwould be undesirable, in particular when affecting public safetyservices which are time critical.

Since coverage extension is a feature provided by relays 135, a relay135 itself may be very likely located towards the edge of coverage ofthe network, since this is the area where the relay 135 may be expectedto serve a larger number of remote UEs 130 whilst also being withincoverage of a base station 120. Thus, a relay 135 itself may bevulnerable to losing network service itself due to mobility of the relay135 and/or changes in network conditions affecting coverage of the basestation 120. When the relay 135 completely loses service from thenetwork, all remote UEs 130 associated with the relay 135 also losenetwork service at this point. Even if the remote UEs 130 are able toregain coverage by associating with another relay 135, there is still aservice interruption, which may not be desirable for time-criticalpublic safety applications (e.g., MCPTT).

Another cause of service interruption may be movement of the relay 135between base stations 120 (and the associated handover procedure). Aswell, the relay 135 may be vulnerable to changing conditions on theradio interface with the base station 120, which may result in the relay135 initiating reestablishment procedures with the base station 120(e.g., due to handover failures or due to fluctuations in serving cellradio link quality). Again, these situations may result in serviceinterruption and/or temporary latency to the services that the relay 135relays to its associated remote UEs 130, which again may be undesirable,especially for public safety services.

Service interruptions may also be caused by conditions in the relay 135itself. The relay 135, even if it remains in good radio conditions withthe network, may enter a state where it may be unable to sustainsidelink operations with its associated remote UEs 130. This may forinstance happen when the relay 135 enters a low battery state, when itstransmission capabilities are deactivated or impaired, or the device isdeactivated for any reason. Again, the resulting service interruptionmay be undesirable, especially for public safety services.

In various examples, the present disclosure may help to mitigate oravoid such service interruptions. This may be done by detecting when aservice interruption is expected or likely to occur (e.g., by detectingone or more trigger conditions), then informing the appropriate entity(e.g., remote UEs 130, base station 120 and/or relay 135) of theexpected service interruption and/or the detected trigger condition(s).This may be carried out prior to actual occurrence of the event causingthe service interruption, which may enable reduction or minimization ofservice interruption. As will be described in the examples providedbelow, the expected service interruption may be detected by the basestation 120, the relay 135, the remote UEs 130, or a combinationthereof.

FIG. 3A is a signaling diagram illustrating an example method formanaging a communication link, in which the indicator(s) of an expectedservice interruption is detected by the relay 135. Although FIG. 3Ashows a single remote UE 130 and is described with respect to a singleremote UE 130, the signaling may be extended to all remote UEs 130associated with the relay 135. As previously described, the relay 135may be in communication with the base station 120 over a Uu link, andmay be in communication with the UE 130 over sidelink channels over aPC5 link, for example.

At 305, the relay 135 may detect one or more indicators of an expectedservice interruption associated with at least one of the communicationlinks, namely at least one of the communication link between the relay135 and the base station 120 (or more generally the network) and thecommunication link between the relay 135 and the remote UE 130.

The indicator(s) that may be detected by the relay 135 may includeindicator(s) related to the communication link between the relay 135 andthe base station 120 (or more generally the network). This may includedetection of degradation of the radio link on the Uu interface, forexample a measure of serving cell quality (e.g., reference signalreceived power (RSRP), reference signal received quality (RSRQ) orchannel quality indicator (CQI)) dropping below a predeterminedthreshold. The relay 135 may also detect that radio link failure (RLF)is imminent (e.g., receipt of at least a predetermined number ofout-of-sync indications, or a timer indicative of imminent radio linkfailure is active). The relay 135 may also detect that the servicequality of the radio link quality or strength on the Uu interface or thePC5 interface has degraded below a predetermined threshold (e.g., anapplication or underlying protocol such as packet data convergenceprotocol (PDCP) or radio link control (RLC) detects that the quality ofthe received service has degraded below a predetermined threshold,detection of a predetermined amount (e.g., predetermined number orpercentage) of missed or un-decoded voice frames, data frames or packetspertaining to a media, or detection that other key parameters such as anerror rate, such as the residual bit error rate on the applicationpackets, has exceeded a predetermined threshold). The relay 135 may alsodetect that it is at an edge of coverage by the network (e.g., detectionof service degradation while also determining there is no suitableneighbor cell that can provide the service of interest and/or detectedbased on neighbor cell measurements). The relay 135 may determine thatnone of the detected cells, including the serving cells and neighborcells on the measured frequencies, have good quality service (e.g., thereceived power of the cells may be below a predetermined threshold).Other example indicators detectable by the relay 135 may include a dropin throughput on the Uu link or the PC5 link below a predeterminedthreshold, a loss of one or more network services from the serving cell(and possibly other neighbor cells which might be candidates forhandover), and a trigger of a handover by the base station 120 or of areestablishment by one or more associated UEs 130, among others. For theabove quality/strength measurements, degradation may be detected if ameasurement drops below a predetermined quality threshold. Thepredetermined threshold(s) may be set according to standards, manuallyset and/or preconfigured in the relay 135 (e.g., preconfigured in theuniversal integrated circuit card (UICC), for example.

The indicator(s) that may be detected by the relay 135 may also includeindicator(s) related to local conditions at the relay 135, and which maynot be related to the communication link between the relay 135 and thenetwork. For example, the relay 135 may detect that the relay 135 isentering a state unable to maintain the communication link with the UE130. Such a state may include, for example, battery power of the relay135 falling below a predetermined threshold, processing power of therelay 135 below a predetermined threshold, the relay 135 having receivedinstructions (e.g., from the user or from higher layers) to turn offpower or stop relay mode of operation, the relay 135 stopping relay ofcertain services (e.g., due to higher layer input or user intervention),relay 135 being overloaded, and the distance of separation or therelative velocity between the relay 135 and the UE 130 being greaterthan a predetermined threshold, among others. Such local conditions atthe relay 135 may impact the ability of the relay 135 to provide therequired service(s) over the PC5 link.

At 310, the relay 135 may transmit a message to the remote UE 130indicating that a service interruption is expected to occur. Forexample, this message may be transmitted prior to actual occurrence ofthe service interruption, and may be transmitted before the servicedegradation is noticeable by the remote UE 130. This message may betransmitted to all remote UEs 130 associated with the relay 135, inwhich case the message may be a broadcast or multicast message on asidelink channel. In other examples, the message may be transmitted toonly those remote UEs 130 which may be affected. Although not shown, insome examples the relay 135 may transmit the same or similar message tothe base station 120, which may enable the base station 120 to initiateappropriate measures to reduce service interruption at remote UEs, forexample by setting up a new relay as described further below.

The transmitted message may include information indicating theindicator(s) of expected service interruption that was detected by therelay 135. In some examples, if the relay 135 is aware of one or moreother relays in its proximity (e.g., discovered by direct discovery bythe relay 135 or identified by the base station 120), information aboutthe other relay(s) may be included in the message. This informationabout other relay(s) may be used by the remote UE 130 in discovering andassociating with a target relay, as described further below.

An example of the transmitted message at 310 is provided in FIG. 3B, inAbstract Syntax Notation One (ASN.1) notation language. In this example,the message may be denoted as serviceDisruptionLikelyIndication (themessage may alternatively be denoted as serviceDisruptionLikelyToOccur,serviceDisruptionExpectedIndication, or other appropriate names, forexample), and the example fields may include:

triggerCause_—indicates the cause for initiating the message. Values mayinclude: rlf (RLF is imminent); rsrqLow (RSRQ of serving cell is below apredetermined threshold); edgeOfCoverage (serving cell quality is belowa predetermined threshold whilst no suitable neighbor cell found);reestablishment (Reestablishment procedure initiated by the relay);lowBattery (battery level of the relay is below a predeterminedthreshold); serviceUnavailable (sidelink service is unavailable);unrSwitchOff (relay is being switched off); and relayModeStop (relay hasbeen reconfigured to stop acting as a relay). Other values may bepossible.

targetUnrList—indicates a list of other relay(s) ProSe UE identity(e.g., the destination which is identified by the ProSe Layer-2 ID asspecified in 3GPP TS 23.303) which may be used by the remote UE 130 toreselect a relay for service continuity reasons. This also may indicatethe physical layer sidelink synchronization identity of the other relay.

The transmitted message may cause the remote UE 130, at 315, to initiateone or more actions to reduce or avoid the expected serviceinterruption. The possible action(s) by the remote UE 130 will bedescribed further below, with reference to FIG. 6.

In some cases, conditions may improve such that service interruption isnot longer expected. At 320, the relay 135 may determine that thepreviously expected service interruption is no longer expected. Forexample, the relay 135 may detect that the indicator(s) detected at 305is(are) no longer valid (e.g., the Uu link quality has improved orhandover was successful).

If so, at 325, the relay 135 may transmit a subsequent message to theremote UE 130 indicating that the service interruption is no longerexpected. In some examples, this subsequent message may includeinformation indicating the reason why service interruption is no longerexpected. This message may also be transmitted to the base station 120(e.g., if the first message indicating expected service interruption wasalso transmitted to the base station 120 at 305).

This subsequent message may cause the remote UE 130, at 330, to cancelthe action(s) that it had initiated at 315. If the remote UE 130 hadalready completed the action(s) and had already disassociated from therelay 135 (e.g., as discussed further below with reference to FIG. 6),the remote UE 130 may not receive this subsequent message or may ignorethis subsequent message.

FIG. 4 is a signaling diagram illustrating an example method formanaging a communication link, in which the indicator(s) of an expectedservice interruption is detected by the base station 120. Although FIG.4 shows a single remote UE 130 and is described with respect to a singleremote UE 130, the signaling may be extended to all remote UEs 130associated with the relay 135. As previously described, the relay 135may be in communication with the base station 120 over a Uu link, andmay be in communication with the UE 130 over a PC5 link, for example.

At 405, the base station 120 may detect one or more indicators of anexpected service interruption associated with at least one of thecommunication links, namely at least one of the communication linkbetween the relay 135 and the base station 120 (or more generally thenetwork) and the communication link between the relay 135 and the remoteUE 130.

The indicator(s) detected by the base station 120 may include thosedetectable by the relay 135, as described above with respect to FIG. 3A.For example, the indicator(s) detected by the base station 120 mayinclude indication that the Uu link quality is below a predeterminedthreshold, indication that the base station 120 has initiated or isabout to initiate the handover phase for the relay 135, and receipt of areestablishment request from the relay 135, among others. Theindicator(s) detected by the base station 120 may also includeindicator(s) of conditions local to the relay 135, in which caseinformation about the local conditions may be provided to the basestation 120 by the relay 135 itself, for example in a message from therelay 135 to the base station 120 (not shown) prior to detection of theindicator(s) by the base station 120.

At 410, the base station 120 may transmit a message to the relay 135indicating that a service interruption is expected to occur. Forexample, this message may be transmitted prior to actual occurrence ofthe service interruption, and may be transmitted before the servicedegradation is noticeable by the relay 135 and/or the remote UE 130.This transmitted message may be similar to that described above withrespect to FIG. 3A (e.g., the example serviceDisruptionLikelyIndicationmessage).

In some examples, the base station 120 may identify one or more UEs inits coverage area suitable to serve as a new relay, and, if the UE isnot already functioning as a relay, may instruct reconfiguration of theidentified UE(s) to serve as a new relay. Information about theidentified target relay(s) may be included in the transmitted message,for example as described above with respect to FIG. 3A.

The message transmitted by the base station 120 may cause the relay 135,at 415, to relay the same message or transmit a similar message to theremote UE 130, indicating that a service interruption is expected. Forexample, the message transmitted by the base station 120 at 410 mayinclude instructions to cause the relay 135 to propagate the messageover sidelink channels over a PC5 interface to all associated remote UEs130, or to those remote UEs 130 which may be affected. The message fromthe base station 120 may also identify the remote UE(s) 130 to which themessage should be propagated.

The transmitted message may cause the remote UE 130, at 420, to initiateone or more actions to reduce or avoid the expected serviceinterruption. The possible action(s) by the remote UE 130 will bedescribed further below, with reference to FIG. 6.

In some cases, conditions may improve such that service interruption isnot longer expected. At 425, the base station 120 may determine that thepreviously expected service interruption is no longer expected. Forexample, the base station 120 may detect that the indicator(s) detectedat 405 is no longer valid (e.g., the Uu link quality has improved therelay 135 informs the base station 120 that its local conditions haveimproved).

If so, at 430, the base station 120 may transmit a subsequent message tothe remote relay 135 indicating that the service interruption is nolonger expected. In some examples, this subsequent message may includeinformation indicating the reason why service interruption is no longerexpected.

The subsequent message may cause the relay 135, at 435, to transmit thesame or similar message to the remote UE 130, indicating that serviceinterruption is no longer expected. For example, the message transmittedby the base station 120 at 430 may include instructions to cause therelay 135 to propagate the message over a sidelink channel to the remoteUE 130.

This subsequent message may cause the remote UE 130, at 440, to cancelthe action(s) that it had initiated at 420. If the remote UE 130 hadalready completed the action(s) and had already disassociated from therelay 135 (e.g., as discussed further below with reference to FIG. 6),the remote UE 130 may not receive this subsequent message or may ignorethis subsequent message.

FIG. 5A is a signaling diagram illustrating an example method formanaging a communication link, in which the indicator(s) of an expectedservice interruption is detected by the remote UE 130. Although FIG. 5Ashows a single remote UE 130 and is described with respect to a singleremote UE 130, the signaling may be extended to all remote UEs 130associated with the relay 135. As previously described, the relay 135may be in communication with the base station 120 over a Uu link, andmay be in communication with the UE 130 over a sidelink channel.

At 505, the relay 135 may transmit a status report to the remote UE 130providing information indicating the quality of the communication linksand/or indicating one or more parameters which may impact the quality ofthe communication links, such as local conditions at the relay 135and/or other parameters, for example as described below. Thecommunication links about which information is provided may include atleast one of the communication link between the relay 135 and the basestation 120 (or more generally the network) and the communication linkbetween the relay 135 and the remote UE 130. The status report may betransmitted automatically by the relay 135, at intervals (which may bevariable, for example depending on the quality of the communicationlink, such as greater frequency as the quality decreases), transmittedin response to changes in communication link conditions (e.g., only if aparameter related to quality of a communication link falls below apredetermined threshold), or as instructed by the base station 120, forexample.

Information provided in the status report may include informationrelated to any of the indicators described above with respect to FIG. 3A(e.g., including Uu-related parameters as well as parameters local tothe relay 135).

An example of the status report transmitted at 505 is provided in FIG.5B, in ASN.1 notation language. In this example, the message may bedenoted as unrStatusReport, and the example fields may include:

uuRsrq—indicates the measured RSRQ over the Uu link

uuRsrp—indicates the measured RSRP over the Uu link

uuCqi—indicates the measured CQI over the Uu link

uuTputUi—indicates the measured throughput over the Uu in uplinkdirection

uuTputDI—indicates the measured throughput over the Uu in downlinkdirection

unrBatteryLev—indicates the battery level at the relay

targetUnrId—indicates the Prose layer 2 ID of one or more UEs which maybe reselected and used as a relay by the remote UEs for servicecontinuity purposes

At 510, the remote UE 130 may determine whether a service interruptionis expected. This determination may be made based on the informationprovided in the status report. For example, if at least one parameterincluded in the status report falls below a predetermined orpreconfigured threshold and/or fails to satisfy a predetermined orpreconfigured criterion. The predetermined threshold may define a valuefor a quality measure (e.g., the measured RSRQ, measured RSRP, measuredCQI, etc.) below which a service interruption is determined to beexpected, for example. The predetermined threshold(s) and/orpredetermined criterion(a) may be pre-coded into each remote UE 130 ormay be specified in the specifications, for example.

In some examples, each remote UE 130 may define its own set ofthreshold(s) and/or criterion(a) for determining whether a serviceinterruption is expected. For example, a remote UE 130 that isconsidered to be of higher priority or considered to be more timesensitive may define threshold(s) and/or criterion(a) that willdetermine a service interruption is expected in conditions that may betolerated (and thus not determined to be indicative of an expectedservice interruption) by a lower priority or less time sensitive remoteUE 130. In some examples, the threshold(s) and/or criterion(a) may bedefined based on the application or service being served over thecommunication link. For example, if the application being served to theremote UE 130 is highly delay sensitive or otherwise sensitive toservice interruptions (e.g., real-time voice or video transmissions formission critical applications), the threshold(s) and/or criterion(a) maybe set to be less tolerant to service degradations (e.g., higherthreshold(s)), compared to another service that may be more delaytolerant (e.g., offline file download).

Thus, each remote UE 130 may make its own determination of whether aservice interruption is expected and may, accordingly, take appropriateaction(s), at different points in time, in response to the same set ofinformation in the status report.

At 515, when it is determined that at least one parameter is below apredetermined threshold and/or fails to satisfy a predeterminedcriterion, the remote UE 130 may initiate one or more actions to reduceor avoid the expected service interruption. The possible action(s) bythe remote UE 130 will be described further below, with reference toFIG. 6.

In some examples, if the remote UE 130 has not yet disassociated fromthe relay 135, the relay 135 may continue to transmit status reports tothe remote UE 130 even after the UE 130 has initiated the action(s) toreduce or avoid the expected service interruption.

In some cases, conditions may improve such that service interruption isno longer expected. At 520, a status report from the relay 135 mayinclude updated information.

At 525, the remote UE 130 may determine that the updated informationindicates that the service interruption is no longer expected. Forexample, the updated information may include an updated parameter thatis no longer below the predetermined threshold or that now satisfies thepredetermined criterion (e.g., a measure of the Uu link quality hasincreased).

Similarly to 510, the determination that the service interruption is nolonger expected may be carried out individually by each remote UE 130,according to individually set threshold(s) and/or criterion(a).Accordingly, a less delay sensitive remote UE 130 may determine that theservice interruption is no longer expected while a more delay sensitiveremote UE 130 may not.

If the service interruption is determined to be no longer expected, theremote UE 130, at 530, may cancel the action(s) that it had initiated at515. If the remote UE 130 had already completed the action(s) and hadalready disassociated from the relay 135 (e.g., as discussed furtherbelow with reference to FIG. 6), the remote UE 130 may not receive theupdated status report transmitted at 520 or may ignore the updatedstatus report.

FIG. 6 is a signaling diagram illustrating example action(s) that may betaken by a remote UE 130 to reduce or avoid an expected serviceinterruption. In this example, the remote UE 130 takes action to attemptto associate with a target relay 140, in order to reduce or avoid theexpected service interruption at its current relay 135.

At 605, the remote UE 130 may perform discovery (e.g., ProSe directdiscovery) to find one or more target relays and/or suitable UEs thatmight potentially operate as a relay or that can be configured tooperate as a relay. In some examples, discovery to find target relaysand discovery to find suitable UEs that might potentially operate as arelay or that can be configured to operate as a relay may be performedindependently. In some examples, information from the relay 135 and/orthe base station 120 (e.g., information provided in the status reportand/or provided in the transmitted message indicating an expectedservice interruption, as described above) may be used by the remote UE130 to prioritize discovery and/or selection of a target relay orsuitable UE. For example, details such as the physical SLSSID or ProSEUE ID of a suitable UE may be provided to the remote UE 130. In someexamples, any nearby relay may be configured to broadcast relay-relatedparameters (e.g., synchronization signals identifying itself as a relay,for example one or more values or a range of pre-configuredphysical-layer side-link synchronization identity(ies) such as SSID),which may help to improve efficiency of the discovery. For example, arelay may broadcast such information in the sidelink master informationblock (MIB-SL), which may help the remote UE 130 to more efficientlyidentify and select a target relay. The MIB-SL may provide informationgenerally applicable for direct discovery of relays. The MIB-SL may alsocontain other information about the relay, such as a list of MCPTTgroups which the relay is currently serving and a list of APNs to whichthe relay is currently forwarding traffic, for example. In someexamples, any UE discoverable by the remote UE 130 might potentiallyoperate as a relay or can be configured to operate as a relay. In someexamples, only some UEs discoverable by the remote UE 130 mightpotentially operate as a relay or can be configured to operate as arelay. In some examples, any UE pertaining to the same group (e.g. anMCPTT group) as the remote UE 130, might potentially operate as a relayor can be configured to operate as a relay.

If one or more target relays and/or suitable UEs are found, the remoteUE 130 may select one target relay or suitable UE to serve as its newrelay. In some examples, selection of the one target relay or suitableUE may be based on information provided by the message (e.g., aserviceDisruptionLikelyIndication message) from the current relay 135that indicated the expected service interruption.

In some cases, the remote UE 130 may select a suitable UE that is notyet configured to operate as a relay. For example, there may be nonearby UEs that are already configured as relays, or the discoverednearby relays are unable to provide the service required by the remoteUE 130. In such a case, the remote UE 130 may, at 610, transmit arequest to its current relay 135 requesting configuration of theselected UE to serve as a new relay.

At 615, the current relay 135 may transmit the request for configurationof a new relay to the base station 120.

At 620, the base station 120 may transmit a message to the selected UEto cause the UE to begin the relay mode of operation.

The message from the base station 120 may cause the selected UE, at 625,to begin operation as a relay.

At 630, after the target relay 140 has been selected by the remote UE130 (and optionally after configuration of a suitable UE to operate as arelay, if applicable) the remote UE 130 and the target relay 140 mayundertake appropriate interactions to cause the remote UE 130 toassociate with the target relay 140. This may include the remote UE 130disassociating from its previous relay 135.

Optionally, at 635, after the remote UE 130 successfully associates withthe relay 140, the remote UE 130 may inform the previous relay 135 ofthe association with the relay 140. This information may be used by theprevious relay 135 to update its list of currently associated UEs, forexample.

The action(s) performed by the remote UE 130, as described withreference to FIG. 6, may be cancelled at any time if the remote UE 130receives a message indicating that service interruption at its currentrelay 135 is no longer expected or if the remote UE 130 determines thatservice interruption at its current relay 135 is no longer expected.

In some examples, the remote UE 130 may not associate with another relayprior to actual service interruption at its current relay 135. Forexample, the remote UE 130 may not find any target relay or suitable UEin its proximity. If the relay 135 loses network coverage and still hasone or more remote UEs 130 associated to it, the relay 135 may enableDMO-R operation and become a UUR, for example. FIG. 7 is a signalingdiagram illustrating an example method for managing a communicationlink, for the above-described scenario. Although FIG. 7 shows a singleremote UE 130 and is described with respect to a single remote UE 130,the example method may apply to all remote UEs 130 associated with therelay 135 that do not associate with another relay prior to actualservice interruption. As previously described, the relay 135 may be incommunication with the base station 120 over a Uu link, and may be incommunication with the UE 130 over sidelink channels over a PC5 link,for example.

The example method of FIG. 7 may include 305, 310 and 315, as describedwith respect to FIG. 3A above, for example.

At 720, the relay 135 may lose network coverage (e.g., losescommunication with the base station 120). At this point, the relay 135may switch to the UUR mode of operation if there are two or more remoteUEs 130 still associated or linked in communication with the relay 135.Alternatively, the relay 135 may switch to a direct mode of operation(e.g., DMO), where the relay 135 directly communicates with the remoteUE 130, if there is only one remote UE 130 still associated with therelay 135. In general, the relay 135 may function as a UUR or as a UE indirect mode of operation with a remote UE 130, depending on the numberof remote UEs 130 that remain associated with the relay 135.

At 725, the action(s) initiated by the remote UE 130 to reduce or avoidthe expected service interruption may fail. For example, the remote UE130 may be unable to find a target relay or suitable UE to switch to.Accordingly, the remote UE 130 may remain associated with the relay 135.Although 725 is shown after 720, 725 may occur anytime after 315, andmay occur prior to 720.

At 730, after the relay 135 switches to the UUR mode of operation oralternatively switches to a direct mode of operation, the relay 135 maytransmit a message to any remote UEs 130 that are still associated,indicating that the relay 135 is in a limited service state. Thismessage may indicate to the associated remote UE(s) 130 that thenetwork-based service(s) is(are) no longer available. In some examples,this message may also indicate the service(s) that the relay 135 isstill able to support. For example, to support public safety services,the relay 135 may, upon switching to operation as a UUR, start a newMCPTT server locally to facilitate communication among associated remoteUEs 130 via the relay 135.

At 735, the remote UE 130 may switch to the service(s) that are stillprovided by the relay 135.

In some examples, the switch from operation as a UNR to operation as aUUR, the use of DMO-R mode instead of NMO-R mode and/or the switch to adirect mode of operation may require preauthorization and/orpre-configuration for the relay 135 and/or the remote UE 130.

The example method described above may enable the remote UEs 130 stillin association with the relay 135 to maintain communication with eachother (e.g., for local mission critical communications) even after thecommunication link between the relay 135 and the network fails. If, at alater time, the relay 135 regains network coverage, it may return toNMO-R operation and function as a UNR for its associated remote UEs 130.

The above discussions provide examples of the relay 135 initiallyoperating as a UNR. However, it should be understood that the abovediscussions may be similarly applicable (e.g., with suitablemodification) to cases where the relay 135 operates as a UUR from thestart. In such a case, FIGS. 4 and 7 may not be applicable, and FIGS. 3Aand 5A may be applicable with the modification that only thecondition(s) relevant to the communication links between the relay 135and its associated remote UE(s) 130 are considered.

Although the present disclosure describes methods and processes withsteps in a certain order, one or more steps of the methods and processesmay be omitted or altered as appropriate. One or more steps may takeplace in an order other than that in which they are described, asappropriate.

While the present disclosure is described, at least in part, in terms ofmethods, a person of ordinary skill in the art will understand that thepresent disclosure is also directed to the various components forperforming at least some of the aspects and features of the describedmethods, be it by way of hardware components, software or anycombination of the two, or in any other manner. Moreover, the presentdisclosure is also directed to a pre-recorded storage device or othersimilar non-transient computer readable medium including programinstructions stored thereon for performing the methods described herein,including DVDs, CDs, volatile or non-volatile memories, or other storagemedia, for example.

The present disclosure may be embodied in other specific forms withoutdeparting from the subject matter of the claims. The described exampleembodiments are to be considered in all respects as being onlyillustrative and not restrictive. Selected features from one or more ofthe above-described embodiments may be combined to create alternativeembodiments not explicitly described, features suitable for suchcombinations being understood within the scope of this disclosure.

All values and sub-ranges within disclosed ranges are also disclosed.Also, while the systems, devices and processes disclosed and shownherein may comprise a specific number of elements/components, thesystems, devices and assemblies could be modified to include additionalor fewer of such elements/components. For example, while any of theelements/components disclosed may be referenced as being singular, theembodiments disclosed herein could be modified to include a plurality ofsuch elements/components. The subject matter described herein intends tocover and embrace all suitable changes in technology. All referencesmentioned are hereby incorporated by reference in their entirety.

1-20. (canceled)
 21. A method for managing continuity of a communicationservice, the method comprising: detecting, at a first relay, anindicator of a change to a condition related to maintenance of at leastone of: a first radio communication link between the first relay and acommunication target, and a second radio communication link between thefirst relay and a first User Equipment (UE); and transmitting, by thefirst relay to the first UE, a first message indicative of the changedcondition, wherein the first message is configured to cause the first UEto initiate a procedure for selecting a second relay to provide thecommunication service.
 22. The method of claim 21, wherein thecommunication target is a network.
 23. The method of claim 21, whereinthe communication target is a second UE.
 24. The method of claim 21,wherein the condition comprises one or more of: a quality of a servingcell signal, a strength of the serving cell signal, a quality of a voiceor a data service, a mobility condition, a velocity condition, and anability to maintain the first or the second radio communication linkdepending on local conditions.
 25. The method of claim 21, wherein theindicator comprises one or more of: an indicator of a battery level, anindicator of a processing power, an indicator of a processing load, anindicator of a condition to switch power off or to stop a relay mode ofoperation, an indicator of a condition for stopping relaying of one ormore predetermined services, and an indicator of a distance ofseparation or of a relative velocity between the first relay and thefirst UE.
 26. The method of claim 21, wherein the indicator is a secondmessage received from the communication target.
 27. The method of claim26, wherein the second message includes an indication of a handover orof a reestablishment.
 28. The method of claim 21, wherein the firstmessage is configured to cause the first UE to initiate the procedurefor selecting the second relay by performing a discovery to find atleast one target relay or one UE suitable to serve as a new relay forthe first UE.
 29. The method of claim 21, wherein the first message isconfigured to cause the first UE to initiate the procedure for selectingthe second relay by identifying at least a target relay or a UE suitableto serve as a relay and establishing a new communication link betweenthe first UE and the target relay or the suitable UE.
 30. The method ofclaim 21, wherein first message includes information useable by thefirst UE for selecting the second relay.
 31. The method of claim 21,wherein the first message is configured to cause the first UE to selectthe second relay based on information broadcast by one or more candidaterelays.
 32. The method of claim 29, further comprising: receiving, atthe first relay, a third message from the first UE for requesting aconfiguration of the suitable UE as the second relay.
 33. The method ofclaim 29, further comprising: transmitting, by the first relay, a fourthmessage to the communication target for requesting the configuration ofthe suitable UE as the second relay.
 34. The method of claim 21, furthercomprising: subsequent to transmitting the first message indicative ofthe changed condition, transmitting, by the first relay, a fifth messageindicating that the changed condition is no longer valid; the fifthmessage being configured to the first UE to cancel the procedure forselecting the second relay.
 35. The method of claim 34, wherein thetransmission of the fifth message by the first relay is triggered byreception of a sixth message received from the communication target. 36.A system for managing continuity of a communication service, the systemcomprising: a communication interface for wireless communication; and aprocessor configured to execute instructions to cause the system to:detect an indicator of a change to a condition related to maintenance ofat least one of: a first radio communication link between a first relayand a communication target, and a second radio communication linkbetween the first relay and a first User Equipment (UE); and transmit,to the first UE, a first message indicative of the changed condition,wherein the first message is configured to cause the first UE toinitiate a procedure for selecting a second relay to provide thecommunication service.
 37. The system of claim 36, wherein the indicatoris a second message received from the communication target.
 38. Thesystem of claim 37, wherein the second message includes an indication ofa handover or of a reestablishment.
 39. The system of claim 36, whereinthe first message includes information useable by the first UE forselecting the second relay.
 40. A non-transitory computer-readablemedium comprising computer-executable instructions that, when executedby a processor of a wireless communication system, causes the system to:detect an indicator of a change to a condition related to maintenance ofat least one of: a first radio communication link between a first relayand a communication target, and a second radio communication linkbetween the first relay and a first User Equipment (UE); and transmit,to the first UE, a first message indicative of the changed condition,wherein the first message is configured to cause the first UE toinitiate a procedure for selecting a second relay to provide thecommunication service.